1. Technical Field
The present invention relates to an image processing apparatus, an image forming apparatus, an image processing method, a computer program and a recording medium for joining an original image, which is obtained by reading an original, with a watermark for copy control, which appears as a result of making a copy.
2. Description of Related Art
Certified copies (e.g., family registers and certificates of residence) published by official agencies on the basis of original documents containing personal information are widely used as papers for authenticating individuals. In order to ensure the function as papers for authenticating individuals, certified copies are required to be distinguished clearly from duplications thereof. Moreover, certified copies published by official agencies require measures to protect privacy, since personal information is contained therein.
Documents printed on the basis of original documents in companies also require measures to protect privacy as well as the certified copies described above, since personal information such as customer information is sometimes contained therein. Moreover, when commercial or technical confidential information is contained in documents created in companies, it is necessary to prevent leakage of the documents to a third party who is under no obligation to keep secrets.
Japanese Patent Application Laid-Open No. 2007-88763(Patent Document 1) discloses a print control unit for causing a computer to join contents data (original image data) indicative of information contained in an original document with watermark data indicative of a watermark for copy control (e.g., an illegal copy warning text such as “COPY”, “DON'T COPY” or “CONFIDENTIAL”), which does not appear in a certified copy or a document but appears in a duplication of a certified copy or a document made by a copying machine, and printing a certified copy or a document on the basis of obtained composite data. The print control unit can cause a computer to join original image data with watermark data and print an image associated with the watermark data and the original image data on normal paper, eliminating the need to use anti-copying and anti-counterfeiting paper having the above-described watermark for copy control printed thereon in advance. Moreover, the user can select easily a watermark appropriate for the information contained in a certified copy or a document. In recent years, an image forming apparatus for reading an original document printed on paper at an image reading unit to generate original image data and joining the generated original image data with prestored watermark data to form an image of a certified copy or a document has also been proposed in view of a case where the original document is not digitized.
Formation of an image of a certified copy or a document by joining original image data with watermark data consumes more recording material than formation of only an original image associated with original image data. Japanese Patent Application Laid-Open No. 2008-22237 (Patent Document 2) discloses an image processing apparatus for forming an explicit watermark over an original image. The image processing apparatus limits an area on paper for printing a watermark so as to reduce the consumption of recording material. The technique of limiting an area on paper for printing a watermark according to Patent Document 2 is considered applicable also to an image forming apparatus for forming a watermark for copy control, which appears as a result of making a copy.